Art of examining quartz



Sept. 7, 1943. J, gg JRX 2,328,968

ART OF EXAMINING QUARTZ Filed July 1, 1942 Simmer Jawplzl'lmi Ctttorneu Patented Sept. 7, 1943 v '2,32 ,9ss

ART OF EXAMINING QUARTZ Joseph F. Eckert, Jr., Philadelphia, Pa., assignor to of Delaware Radio Corporation of America, a corporation ApplicationJuly 1, 1942, sent; No. 449,363

Claims.

. This invention relates to the art of examining quartz and has special reference to a new and improved method of determining the orientation of a quartz bar, cube, or other partly fabricated piece of natural quartz of the type possessing piezoelectric properties.

In the manufacture of piezoelectric elements the crystal blanks are usually sliced from a prefabricated bar, cube or other unfinished quartz piece which may have any one of several orientations with respect to the natural cry talline axes of the mother crystalfrom which it was derived. Ordinarily the bars are cut from the mother crystal with an orientation calculated to provide the maximum useful number of finished elements. By way of example, as disclosed in U. S. Patent 2,264,698 to Charles E.-Johnson, when the mother crystal comprises a small quartz candle," it is preferable first to cut the mother crystal into a bar having long sides parallel to the optic axis and to thereafter slice the semi-finished blanks from the said bar. On the other hand, when the mother crystal is of a diameter substantially greater than, say, 2- inches, the more common practice is to employ a bar or a cube cut from a slab having top and bottom surfaces which lie in planes normal to the optic axis. In

any event, it will be apparent that before the unfinished blanks can be sliced from the larger piece, the lapidary must know the orientation and other characteristics of that particular piece or specimen. Thus, he must know (a) the location of its optic axis, (1)) the virtual location and direction of tilt of the major and/or minor apex faces of the mother crystal from which the specimen was cut, and (0) whether the quartz is of the "right hand" or of the (left hand' variety. He should also preferably be informed as to the polarity of the X-axes in the said piece of quartz.

All, or at least some, of thisinformation must, of course have-originally been available to the lapidary in order to have enabled him to cut the bar itself from the mother crystal. However,

before cutting a bar into blanks it is standard practice to etch the bar (as with hydrofluoric acid) in order to detect twinning," and other defects which, if present, would necessitate dis-- carding the bar.

an etched bar,'cube or other partly fabricated pieceof natural quartz.

Another and related object of the invention is to provide animproved method of locating the optic axis of an etched piece of quartz, and one which in its practice also reveals (a) whether the-said piece is formed of "right han or of 'left han quartz, (b) th virtual location of the direction of tilt of the major and/or minor apex faces of the mother crystal from which the iece was cut, and (c) the polarity and approximate location of the terminals of the X-axes in said piece.

A further object of the present invention is to provide a simplified-method of examining quartz, and one which in its practice obviate the use of messy oils and expensive equipment;

Other objects and advantages will be apparent and the invention itself "will be best understood by reference to the following specification and to the accompanying drawing, wherein Figure 1 is a view in elevation of a quartz bar to which the invention is applicable and showing in outline a side section of the mother crystal from which the said bar was derived,

Figure 2 is a similar view of a quartz bar of another typical orientation, and to which the invention is applicable,

Figure 3 is a partly diagrammatic side elevational view of an apparatus which may conveniently be employed in carrying the invention into effect.

Figures 4 to 7 inclusive show certain patterns of light which appear in the quartz bars of Figs. 1 and 2 when inspected with the apparatus of Fig. 3, and whichwill be referred to in the following speciflcation.

The invention will be described in connection with a problem commonly encountered in the commercial production of piezoelectric crystal elements from oblong bars whose long sides are substantially parallel either to the Z axi or to a Y axis of the mother crystal. It will be apparent, however, as the description proceeds that the invention is likewise applicable to quartz pieces of other shapes and of other orientations.

Fig. 1 shows a bar Q having its long sides substantially parallel to a Y axis and which has been cut in accordance with a standard procedure from fiaws in their natural crystalline structure) and hence are free from any previously applied markings indicative of their orientation. In such a case, it is obvious that before the semi-finished. piezoelectric crystal elements or blanks can be cut fromthe said bars, it will be necessary for the lapidary to know the orientation and crystalline structure of each bar.

A spot source of light is employed in carrying the invention into effect. As shown in Fig. 3, the light may comprise an ordinary electric lamp I employing, say, a 40 watt bulb 2 and with the light therefrom directed upon the quartz piece Q through a pinhole 3 in a masking plate 4. The mask 4 may conveniently comprise either a turntable or a fixed support upon which the specimen rests during its inspection. When, as in the instant case, the piece of quartz to be examined comprises an oblong bar, it may be laid on its side, without clamping pressure, upon the plate 4 so that the spot of light impinges upon its bottom long surface. If the piece. comprises a cube, it may first rest upon any of its surfaces. In accordance with the invention each face of the quartz specimen is presented to the spot of light until one of them reveals to the observer (indicated in Fig. 3 by the eye 5) a light pattern P Fig. 4, P Fig. 5 in the form of a parallelogram having short sides 6 and 8 which intersect the long sides I and 9 at an angle other than a right angle. It has been discovered that the long sides of the parallelogram comprise, or'

are in register with, the optic (Z) axis of the quartz. Thus, to provide a permanent indication of the location of the optic axis it'is merely necessary to draw a line Z-Z (as with a pencil, crayon,-or stylus, not shown) on the specimen parallel to the long sides of the said parallelogram. y

In order to determine whether the quartz is of the "right hand or of the left hand variety, the specimen should first be so oriented with respect to the observer that one of the long sides of the parallelogram is to his right and thepther to his left, as shown by way of example in Fig, 4. (In Fig. 5 wherein the optic axis Z-Z is parallel to the long sides of the specimen, theobserver may either shift his position, or he may move the specimen 90 either in the clockwise or counter-clockwise direction). With the specimen in the desired position the long right side 9 of the parallelogram is used as a reference line. It

- is then necessary to note whether the acute (N. B., as distinguished from obtuse") angle a formed by the intersection of this reference line 9 with one of the short sides (6 or 8) of the parallelogram P lies adjacent to the top or to the.

"bottom of said parallelogram. If the said acute angle is at the top of the parallelogram, the

specimen is constituted of right hand quartz;

and if it is adjacent to the bottom of the parallelogram, it comprises "left hand quartz. Thus the specimen Q, Fig. 4 -i's shown to be right hand quartz and the specimen Q of l ig. 5 comprises left hand quartz. Since, as previously pointed out, any line drawn parallel to the long sides of the light pattern comprises the optic axis of the quartz it is obvious that the line 9 when suitably marked may be utilized as the reference optic axis, in which casethe other line ZZ is superfluous, and need not be marked upon the specimen.

The short sides 6 and 8 of the light pattern reveal the virtual location and direction of tilt, with respect to the optic axis, of a major apex face of the mother crystal from which the speci- 5 men was derived. Accordingly, when this information is requiredto be known the specimen may be permanently marked with such a line, as indicated at MM. In some cases, as where the etching is unduly shallow, or unduly deep,

10 the said short sides of the parallelogram may not provide an exact indication of the location of a major apex face of the mother crystal. This, however, is of no especial moment since (a) the indication of the direction ofslope is the important thing and (b) the exact angle formed by the intersection of a. major or a minor face with the optic axis is known to be approximately 38 14" and, since the direction of slope has been indicated, it is a relatively simple matter to go check the accuracy of the indication provided by the said short sides of the light pattern.

The present invention does not lend itself readily to the accurate location of the X and Y axes of a quartz specimen. However, it may here be noted that the electricallypositive terminal of the X-axes will always lie adjacent to the surface of the specimen upon which the above described parallelogram light pattern appears.

Figs. 6 and 7 show the light patterns which are obtained by directing the spot of light upon the (positive) surface of the crystal upon which the closed parallelograms of Figs. 4 and 5 appear. It will be' observed that the principal diflerence between the patterns shown in Figs. 4

and 6, and in Figs. 5 and 7, resides in the fact that in Figs. 6 and 7 the edges of the light pattern extend beyond the boundaries of the parallelogram. Further, in practice, the latter patterns may not be as clearly defined as the ones 40 shown inFigs. 4 and 5. Accordingly, in practicing the present invention, it is preferable to seek the "closed" light patterns of Figs. 4 and 5 rather than the openwork" or criss-cross" patterns of Figs. 6 and 7, though either may be utilized. If these latter patterns are employed of the mother crystal.

It will now be apparent that the present invention comprises a simple, inexpensive and trouble-free method of examining rapidly a quartzspecimen to determine (a) the location of its optic axis- (b) the virtual location and direction of tilt of the major and minor apex faces of the mother crystal from which the specimen was derived, (c) whether the quartz is of the right han or "left hand variety, and (d) the'locaspecimen.

What is claimed is: 1. Method-of locating the optic axis of an co tion of the positive and negative faces of the etched piece of quartz, said. method comprising 5 directing a spot of light upon different surface areas of said quartz piece until a light pattern in the form of a parallelogram having long and short sides which intersect at an angle other than a right angle is revealed to an observer looking into said piece from the opposite side thereof,

marking on said piece a line drawn parallel to the long sides of said parallelogram, and designating the said line as the optic axis.

2. Method of locating the optic axis and of 7 determining the polarity of the surfaces of an etched piece of quartz, said method comprising directing a, spot of light upon dilferent surfaces form of a parallelogram [having long and short sides whichintersect at an angle other than a right angle is revealed to an observer looking optic axis, of a major apex face of the mother crystal from which said piece was derived, said method comprising directing a spot of light upon different surface areas of said quartz piece until a light pattern in the form of a parallelogram having short sides which intersect the long sides at an angle other than a right angle is revealed to an observer looking into said piece from the opposite side thereof, marking on said surface a line parallel to the long sides, and a second line asses of said quartz piece until} light pattern in the face of the mother crystal from which said quartz piece was derived. a

4. Method of examining an etched piece of quartz to determine whether said quartz is of the right hand" or of the "left han variety, said method comprising directing a spot of light upon various surface areas of said quartz piece until a 'lightpattern in the form of a parallelogram having short sides which intersect the long side at an angle other than a right angle is revealed to an observer looking into the. piece from the opposite side thereof, orienting said quartzpiece with respect to the observer until one of said long sides 'of said parallelogram is to the right and the other long side of said parallelogram is to the left of said observer, designating said long right 'side oi said parallelogram as a reference line, and then. marking'said quartz to be (a) of the "right hand variety or (b) ,of the left hand variety as determined by whether the acute angle formed by theintersection of said reference line.

with one of said short sides of said parallelogram lies'adiacent to (a) the top or (b) to the bottom parallel to the short sides of said parallelogram,

designating said first mentioned line as the optic of said piece, and designating said second .itioned line as a side edge or a major apex of said parallelogram.

5. Method of examining quartz in accordance with the preceding claim and including the additional step of designating said reference line as r the optic (Z) axis of said quartz piece.

JOSEPH F. ECKERT, JR. 

